Method of coating a surface

ABSTRACT

The present invention relates to coating and printing methods for the deposition of aqueous compositions. The composition may be adapted to any method without the need to change its chemical content. Viscosity is determined and adjusted by raising and lowering the temperature. High gloss value, increased film integrity and enhanced mar resistance result.

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 08/029,681, filed Mar. 11, 1993, now U.S. Pat. No.5,384,160, issued Jan. 24, 1995.

FIELD OF THE INVENTION

The present invention relates to a novel method for the deposition ofaqueous coating compositions in printing processes including wet-trap,gravure, offset (waterless or using water), silk-screen, flexography,off-line dry-trap, and related printing processes. In addition, thepresent invention relates to a method for depositing barrier coatings onpaperboard trays and related items for use in the food industry. Thesebarrier coatings are particularly useful for influencing the moisturevapor transition rate (MVTR) and oil and water resistance in paperboardpacking to be used to store moisture sensitive foods.

Use of the present invention allows the adaptation of an aqueous coatingto virtually any printing method without changing the chemical contentof that formulation. The present invention, in certain embodiments,utilizes exceptionally high levels of solids in printing coatingcompositions and unexpectedly obtains acceptable viscosity, flowcharacteristics and mechanical transfer for these compositions. Inaddition, the present invention is readily adaptable to virtually everytype of coating process used to coat inked, uninked and relatedsurfaces. The method according to the present invention may also beadapted for use in the food industry to deposit barrier coatings onpaperboard for food storage in order to influence the MVTR and oil andwater resistance of the underlying packing or storage material.

BACKGROUND OF THE INVENTION

Aqueous coating compositions of a resinous thermoplastic coatingmaterial (clearcoat) such as thermoplastic, (meth)acrylic or(meth)acrylic-styrene copolymer in the form of emulsions are well knownin the printing industry and presently are being used to coat inked anduninked layers during wet-trap, off-line dry-trap, gravure, offset,silk-screen, flexography and related printing or coating processes usingan aqueous coating composition.

In one aspect of the above-referenced printing processes, an ink layeris first put down on a substrate in the form of paper, cloth,fiberboard, corrugated box, etc. and depending upon the process, the inklayer is first allowed to dry before it is coated, or is coated wet. Inother methods according to the present invention, the coating may simplybe placed onto an uninked or ink-free substrate. The aqueous coatingserves to provide certain film characteristics including gloss, marresistance, oil and water resistance, MVTR, and protection of the inked,uninked or related surface, adhesion and other characteristics. Thesefilm characteristics are generally determined by the weight of thecoating applied and the amount or percent of solids used in the coatingcomposition.

The prior art materials used as coatings in combination with the currentprint coating techniques are grossly limited in the solid contents thatmay be uniformly deposited onto a substrate from a coating compositionand the degree of gloss value that a coating may obtain. In addition, aspresently employed, the formulation of one aqueous coating may only beused in one or perhaps two processes; it is virtually impossible usingthe present methods without the present invention to provide oneformulation which may be readily adapted for use in wet-trap, off-linedry-trap, gravure, offset, silk-screen, flexography and other printingprocesses.

In wet-trap in-line printing processes an ink coating (usually ahydrophobic ink) is first deposited onto paper, fiberboard, cardboard,corrugated paper or similar material, as a wet ink and then an aqueouscoating is deposited onto the wet ink layer such that the ink is"trapped" under the aqueous coating to provide adequate filmcharacteristics. In dry-trap off-line printing processes the ink isfirst dried before an aqueous coating is deposited onto the ink layer.

Gravure and flexography printing processes employ plates or etchedcylinders (generally containing inverted pyramids) to deposit the inklayer (usually a water-based or solvent-based ink) which is generallydried before being coated by an aqueous coating. The result is a smoothfinish without screen or dot pattern. In these applications, it iscritical to have adequate mechanical transfer and flow characteristicsto obtain adequate surface tension and favorable film characteristicsafter deposition.

In offset printing processes, the image to be reproduced is copiedphotographically upon a metal plate with a solution containing water toprevent the ink from adhering to the non-image area. When placed uponthe appropriate cylinder of an offset press, the metal plate is inked inthe image area only and makes an imprint of the image on arubber-covered cylinder, which in turn, prints upon sheets of paperwhich are automatically fed into the machine. After the image has beendeposited onto the paper, it may be coated using an aqueous coating inorder to enhance the physical characteristics of the ink surface. Newertechniques in offset utilize waterless plates which keep the ink fromadhering to the non-image area without the use of water, alcohol orfountain solution.

Silk-screen is a process employing a stencil to print a flat colordesign through a piece of silk or other fine cloth on which all parts ofthe design not to be printed have been stamped out by an impermeablesubstance.

The viscosity and consequently, the flow characteristics and mechanicaltransfer of an aqueous coating composition as used in printingprocesses, are directly influenced by the chemistry of the formulation,in particular, the percentage of solids that are present in thecomposition. In general, as the amount of solids in an aqueous coatingcomposition increases, the mechanical transfer of the coating generallysuffers, because the coating composition becomes too viscous to beefficiently deposited using the techniques presently available in theart. Often, the viscosity of an aqueous composition is the limitingfactor in determining the transfer and the degree of usefulness of thecoating composition. In general, upon application of an aqueous coatingcomposition onto an inked, uninked or related layer, acceptablemechanical transfer will provide for a coating evidencing acceptableflexibility, durability, film-thickness and gloss, among other favorablefilm characteristics. In compositions which are too viscous, i.e., havepoor flow characteristics and thus evidence inadequate mechanicaltransfer, the tendency is to produce a coating which evidences a"ribbing" or an uneven deposition of the coating. Inconsistencygenerally results from a coating having high viscosity.

The standard measure of aqueous coating viscosity in the printingindustry is generally determined using a Zahn cup or equivalent. Zahncups are identified with numbers representing the size of flow holes incups. For example, the #2 cup is designed with a smaller hole than the#3 cup. To determine viscosity, a cup is chosen and then dipped into theaqueous coating composition until it is filled to the top. Thecomposition will exit the cup from the hole depending upon the size ofthe hole and the viscosity of the composition measured. The compositionstream leaving the cup is then timed with a stopwatch until the cupempties. The time that the composition takes to completely exit the Zahncup hole in seconds represents the composition's viscosity. Theviscosities of compositions nay be compared directly based upon theequipment and the mechanical application used. Often the selection of atype of Zahn cup design used is based on the type of printing methodutilized.

It is commonly known in the trade, for example, that the viscosityvalues (measured using a Zahn Drip Cup or equivalent measuring device)necessary for effective mechanical transfer for all printing methodswill vary, based upon the mechanics of that printing process. Forexample, in the case of gravure printing processes, the viscosity for anaqueous coating useful in this process ranges from about 17 to about 28seconds measured with a #2 Drip Cup. Silk screen printing requires aviscosity range of about 12 to about 23 seconds (#2 Drip Cup). In thecase of flexography printing, the viscosity of the aqueous coatingranges from about 20 to about 60 seconds (=2 Drip Cup). In the case ofoffset printing, the viscosity of the aqueous coating ranges from about15 to 30 seconds (#3 Drip Cup). One of ordinary skill will understandthese values to represent exemplary useful ranges for practicing thepresent invention. The actual ranges may vary depending on the equipmentand application used.

Under the present practice in the industry, the method employed forchanging the viscosity of an aqueous coating formulation once it reachesthe printing plant is to change the chemistry of the formulation, i.e.,adjust the viscosity of the formulation by adding resinous material toincrease viscosity or alternatively, by adding solvent to decreaseviscosity. This is a time consuming and inefficient practice, especiallywhere there is a need to use an aqueous coating in more than one type ofprinting process. To avoid this problem, there presently is a need tohave several formulations of aqueous coating on hand, in order toaccommodate the varying mechanical transfer requirements of the variousprinting processes. One aqueous coating formulation will simply notsuffice.

In the present practice, the transfer of the aqueous coating compositionis limited by the viscosity, which is affected by the amount of solidscontained in the composition. As one increases the amount of solids, theviscosity of the aqueous coating also increases. It is generallyrecognized that as the amount of resin in the aqueous coating increases,the gloss, durability, film-thickness and related coatingcharacteristics may tend to increase. Present coatings, however, arelimited in the amount of solids that can be used without so dramaticallyincreasing the viscosity of the coating formulations that they cannot beused in traditional printing processes. The present invention seeks toaddress this limitation to produce coatings having extremely high gloss,durability and film-thicknesses heretofore unknown in the printingindustry using coating compositions which can be easily adapted for usein virtually all printing processes.

One of the major problems facing the printing industry is the need forusing large amounts of volatile organic compounds or VOC's in aqueouscoating compositions. Although a major component of an aqueous coatingcomposition is water, in a majority of cases, in order to producecompositions containing high solid content, VOC's are added to theaqueous composition to lower the viscosity of high solids contentcompositions. At present, it is often not feasible to produce highsolids content aqueous compositions without adding substantialquantities (greater than about 5% by weight) of at least one VOC, suchas ethanol, isopropanol, a ketone, ether or the like. The addition ofthe VOC in present aqueous compositions is known to compatibilize thesolids in the composition, thus producing a less viscous product than isproduced without the VOC. Even with the VOC, however, the amount ofsolids that may be added to a composition is quite limited; the resultis an aqueous coating composition which cannot produce the extremelyfavorable coating characteristics (especially high gloss values incombination with mar resistance, durability and flexibility) which aredesired in today's market and which are produced using the method of thepresent invention.

The present invention may be adapted to provide extremely favorablecoating characteristics, including high gloss value, increased filmintegrity and enhanced mar resistance without having to resort to theinclusion of substantial quantities of VOC's (which is the presentpractice). Thus, it is finally possible to formulate a single coatingcomposition which will exhibit favorable mechanical transfer duringcoating and favorable film characteristics after deposition. This is anunexpected result. Thus, by utilizing the present invention, a singleaqueous composition containing low VOC's or even an absence of VOC's canbe generally adapted to a number of printing methods to provideexceptionally favorable coating and mechanical transfer.

In the food industry, paperboard having a moisture barrier coating hasrecently been used to replace polyboard (for use as food trays andrelated plastic food packaging material) for providing MVTR and oil andwater resistance in storing food. In its present form, a moisturebarrier coating (in preferred embodiments also incorporating oil andwater resistance) is coated onto the surface of the paperboard so as toultimately create a surface which can influence the moisture vaportransition rate and lower it to a level which is compatible with thestorage of food, especially meat, poultry and other perishable items.Presently however, in order to create a coating thick enough or denseenough to materially impact the moisture vapor transition rate, anaqueous coating solution must be applied at least two or three times ona paperboard surface and subsequently dried. This has created greatinefficiency in producing food packaging material and a clear need inthe art exists for a process which can produce an adequate barriercoating on paperboard in only one coat. The method according to thepresent invention may be used to provide a barrier coating on paperboardin only one application, unlike the prior art methods.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a method fordepositing an aqueous coating composition onto an ink or uninked surfacein numerous printing processes including wet-trap, off-line dry-trap,gravure, offset, silk-screen, flexography and related printing processeswithout having to alter the chemistry of the aqueous coatingcompositions used in that printing process.

It is an additional object of the present invention to provide a methodfor depositing an aqueous coating composition onto a wet or dry inksurface in numerous printing processes without having to alter thechemistry of the aqueous coating composition.

It is still a further object of the present invention to provide amethod for depositing a high solids content aqueous coating compositionexhibiting favorable mechanical transfer onto an inked or uninked layerin numerous printing processes.

It is yet another object of the present invention to provide a methodfor depositing an aqueous composition containing no more than about 5%by weight VOC's onto an ink layer in numerous printing processes.

It is still another object of the present invention to provide a methodfor depositing an aqueous composition containing an absence of VOC'sonto an ink layer in numerous printing processes.

It is yet still an additional object according to the present inventionto provide a barrier coating on paperboard to be used in the foodindustry in one application, by depositing an aqueous coatingcomposition on the paperboard and allowing the coating composition todry.

Still an additional object of the present invention resides in theability to provide coatings on a number of surfaces which vary greatlyin componentry and coating characteristics.

These and other objects of the present invention may be readily gleanedfrom the description of the present invention which follows.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a method for depositing an aqueouscoating composition in the form of a solution, dispersion or emulsiononto an inked or uninked layer in a printing process such as wet-trap,off-line dry-trap, gravure, offset (water or waterless), silk-screen,flexography and other printing processes such that a single aqueouscoating composition may be adapted easily for use in a number ofprinting processes under typical or standard printing conditions withoutthe need for chemical modification of the aqueous coating compositionused in that printing process. Thus, according to the present invention,a single aqueous coating composition may be adapted for use in printingprocesses requiring vastly different viscosities.

In accordance with one aspect of the present invention, the method isdirected to coating a substrate (inked or uninked) and comprises thesteps of:

1). Depositing a first layer of ink onto a surface to be coated;

2). Drying said ink layer;

3). Determining a desired viscosity of an aqueous coating composition tobe deposited onto said ink layer and/or said uninked surface;

4). Determining the temperature other than at ambient temperature atwhich said composition attains the viscosity determined in step 3);

5). Maintaining the viscosity of said composition at the temperaturedetermined in step 4); and

6). Depositing onto said ink layer and/or said surface said aqueouscoating composition at said set temperature.

The present method also relates to a wet-on-wet printing process forcoating an inked and/or uninked surface. This method comprises the stepsof:

1). Depositing a first layer of hydrophobic ink onto a surface to becoated;

2). Determining a desired viscosity of an aqueous coating composition tobe deposited onto said ink layer and/or said uninked surface;

3). Determining the temperature other than at ambient temperature atwhich said composition attains the viscosity determined in step 2);

4). Maintaining the viscosity of said composition at said temperaturedetermined in step 3); and

5). Before said ink layer is dry, depositing onto said ink layer and/orsaid surface said aqueous coating composition at said set temperature.

The present invention also relates to a process for enhancing the solidscontent of a coating to instill favorable film characteristics,including high gloss, film integrity and mar resistance without causingundesirable flow characteristics and mechanical transfer. This methodallows for the incorporation of unexpectedly high levels of solids incoating compositions used to coat inked and/or uninked surfaces inprinting processes. In this aspect the present method comprises thesteps of:

1). Preparing a high solids content aqueous coating composition forcoating an inked and/or uninked surface in a printing process, saidcomposition having a viscosity above a range useful in said process atambient temperature, said composition comprising:

a. at least about 5%, preferably at least about 10% and most preferablyat least about 20% by weight of a low molecular weight film-formingpolymer or resin;

b. at least about 5%, preferably at least about 10% and most preferablyat least about 20% by weight of a high molecular weight film-formingpolymer or resin;

c. an amount of a wetting agent effective to eliminate leveling problemscaused by surface tension; and

d. the remainder of the composition comprising an aqueous solvent ormixture of solvents;

2). Depositing a first layer of ink onto a surface to be coated;

3). Determining a desired viscosity of said aqueous coating compositionto be deposited onto said ink layer and/or said uninked surface;

4). Determining a temperature above ambient temperature at which saidcomposition attains the viscosity determined in step 3);

5). Maintaining the viscosity of said composition at said temperaturedetermined in step 4) to allow deposition of said composition; and

6). Depositing onto said ink layer or uninked surface said aqueouscoating composition at said set temperature.

The present invention also relates to a process for coating an inkedand/or uninked surface using an aqueous coating composition containingless than about 5% by weight VOC's, preferably an absence of VOC's. Inaccordance with this aspect, the present method comprises the steps of:

1). Preparing an aqueous coating composition for coating an ink layerand/or uninked surface containing no more than about 5% by weight VOCcomprising:

a. at least about 5%, preferably at least about 10%, and most preferablyat least about 20% by weight of a low molecular weight film-formingpolymer or resin;

b. at least about 5%, preferably at least about 10% and most preferablyat least about 20% by weight of a high molecular weight film-formingpolymer or resin;

c. an amount of a wetting agent effective to eliminate leveling problemscaused by surface tension; and

d. the remainder of the composition comprising a mixture of water andoptionally, at least one solvent in the form of a volatile organiccompound (VOC), the amount of said solvent comprising no greater thanabout 5% by weight of said aqueous coating composition;

2). Depositing a first layer of ink onto a surface to be coated; and

3). Determining a desired viscosity of said aqueous coating compositionto be deposited onto said ink layer and/or said uninked surface;

4). Determining a temperature at which said composition attains theviscosity determined in step 3);

5). Maintaining the viscosity of said composition at said temperaturedetermined in step 4); and

6). Depositing onto said ink layer and/or said uninked surface saidaqueous coating composition at said set temperature.

The present invention also relates to a method for providing a moistureproof barrier coating evidencing MVTR and oil and water resistance on asubstrate, preferably paperboard, for use in the food industrycomprising:

1). Preparing a high solids content aqueous coating composition fordeposition onto a substrate, said composition containing an amount of afilm-forming polymer effective to produce a moisture-proof barriercoating on said substrate after only one application;

2). Determining a desired viscosity of said aqueous coating compositionto be deposited onto said substrate;

3). Determining the temperature above ambient temperature at which saidcomposition attains the viscosity determined in step 2);

4). Maintaining the viscosity of said composition at the temperaturedetermined in step 3); and

5). Depositing onto said substrate said aqueous coating composition atsaid set temperature.

The various methods according to the present invention may be readilyadapted to utilize numerous aqueous compositions containing optionalcomponents including mar or scuff resistant agents, hardening agents,coalescing agents, plasticizing agents and defoaming agents, amongothers, which are added in effective amounts to provide the desiredresults.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides a pictorial representation of a temperature controlvessel or reactor which can be used in the method according to thepresent invention.

FIG. 2 provides a pictorial representation of a system, for employing asingle coating composition in a number of different printing processes,the coating for each of the processes being adapted by adjustingviscosity in each of the four reactors.

DETAILED DESCRIPTION OF THE INVENTION

The term "transfer" or "mechanical transfer" is used throughout thespecification to describe the ability of an aqueous coating compositionto be deposited onto a surface in a printing process. Ease, efficiencyand consistency of deposition are influenced by the viscosity and theflow characteristics of aqueous coating compositions used in the presentinvention. Viscosity is a physical characteristic of aqueous coatingcompositions which dramatically influences the flow characteristics ofthe compositions and consequently, mechanical transfer of thosecompositions in printing processes. As a general rule, by varying theviscosity of a coating composition, one can dramatically influence theflow characteristics and consequently, the mechanical transfer ofcompositions onto inked and uninked substrates pursuant to the presentinvention.

The term "(meth)acrylate or (meth)acrylic" is used throughout thespecification to describe a monomer, polymer or copolymer which is or isderived from acrylic acid, methacrylic acid, esters of these acids ormixtures thereof.

The term "aqueous coating composition" is used throughout thespecification to describe an aqueous composition in the form of asolution, emulsion or dispersion which is capable of being depositedonto and coating an ink layer in a printing process according to thepresent invention. As used in the present invention, an aqueous coatingcomposition contains effective amounts of a low molecular weightfilm-forming polymer, a high molecular weight film-forming polymer, asurfactant or emulsifier and an aqueous solvent, usually a mixture ofwater and at least one additional solvent, generally a volatile organiccompound (VOC), and optionally other components which may affect orimprove coating characteristics. In particularly preferred embodimentsaccording to the present invention, aqueous coating compositions containan absence of VOC's.

The term "volatile organic compound" or "VOC" is used throughout thespecification to describe most volatile solvents other than water whichare used in the aqueous coating compositions according to the presentinvention. VOC's include, for example, methanol, ethanol, isopropanol,acetone, methylethylketone, various esters including methyl acetate,ethyl acetate, propyl acetate, among others, including chlorinatedhydrocarbons, various ethers and alkanes, among others. In preferredembodiments according to the present invention, aqueous coatingcompositions according to the present invention contain no greater thanabout 5% by weight of a VOC and most preferably, an absence of VOC's.

The term "coating" is used to describe the film that remains on the ink,uninked or related surface after deposition and drying of the aqueouscoating composition. Coatings which are conventionally used in thecoatings industry include for example, Blister Card Coatings,characterized primarily by excellent adhesion, heat reaction and fibertear; MAT Coatings, a low gloss coating characterized by a low glossvalue of about 10° to about 30°; Semi-gloss coatings (relatively lowgloss value) characterized by low gloss value of about 30°-40°; BarrierCoatings, characterized by MVTR and water and oil resistance; HeatResistant Coatings; Anti-Porosity Coatings; Mold Resistant Coatings;Heat Resistant Barrier Coatings, characterized by MVTR, water, oil andheat resistance; Over-print Coatings, characterized by high gloss, marresistance, exceptional durability and adhesion and protection of theunderlying substrate; Prime Coatings, characterized by their primercharacteristics including good holdout and minimal absorption; andAlkaline Resistant Coatings, among others. The film characteristics ofthe coatings related to the present invention are determined primarilyby the componentry and amount (or percent) of solids and other additivesused in the aqueous coating composition.

The terms "film-forming polymer" and "film-forming resin" or "resin" areused synonymously throughout the specification to describe the low orhigh molecular weight polymers or resins which are added to the aqueouscoating compositions according to the present invention to instillfavorable film characteristics to the dried coating. Film-formingpolymers for use in the present invention include thermoset resins,thermoplastics, UV-cured film-forming polymers and mixtures of thesefilm-forming polymers or resins.

The present invention relates to methods for depositing aqueous coatingsonto an ink layer to provide adequate film characteristics such as maror scuff resistance, durability, rub resistance and gloss.

In one aspect of the present method, an aqueous coating in the form of asolution, dispersion or emulsion is deposited onto a dry or wet inklayer. When the ink to be coated is dried before the aqueous coatingcomposition is deposited, the ink may be any chemical compositiontypically used in printing, but is preferably insoluble in a hydrophilic(aqueous) solvent and in particular, the polar aqueous solvent orsolvent mixtures used in the aqueous coating compositions according tothe present invention. Thus, the ink coating may be comprised ofhydrophilic or hydrophobic inks as typically used in the printingindustry, with the proviso that the dried ink preferably should not bemiscible with or soluble in the coating composition used to coat the inklayer. Otherwise, the coating may produce smudging or smearing of theink layer during deposition as the coating and ink layer interact, acondition to be avoided if possible. Depending upon the printingprocess, it may be preferred to use hydrophobic inks (wax-free orcontaining wax) or hydrophilic inks to impart favorable characteristicsto the final coated substrate.

In instances where the printing process employs a wet-on-wet process,for example, a wet trap in-line process, the ink used is wet (i.e.,still contains significant amounts of solvent) during the deposition ofthe aqueous coating. In this process, it may be preferred to utilize ahydrophobic ink. After deposition of the ink layer, the aqueous coating,preferably in the form of a porous coating, can be deposited onto theink layer. The use of a hydrophobic ink will generally minimize thetendency of the ink to smudge while both layers are still wet, at leastin part.

In the present invention, depending upon the printing process utilized,the amount of ink deposited as the first layer and the amount of aqueouscoating composition deposited as the second layer will vary over a widerange, and consequently the viscosity, flow characteristics andmechanical transfer of the aqueous coating composition will also varyover a rather wide range.

In the present method, the aqueous coating composition may be depositedby any process, including rolling the composition onto the substrate. Byusing the present invention, viscosity is virtually eliminated as acritical characteristic.

The aqueous coating composition used in the present method employs atleast three, and preferably four components:

1) a low molecular weight film-forming polymer or resin solid in anamount effective to provide adequate gloss to the dried coating;

2). a high molecular weight film-forming polymer or resin solid in anamount effective to support the low molecular weight film-formingpolymer and preferably, provide adequate film characteristics includingmar or scuff resistance, rub resistance, durability and film integrityto the dried coating alone or in combination with optional additives;

3) an amount of at least one wetting agent or surfactant effective toeliminate leveling problems caused by surface tension of the coatingduring deposition onto the ink

4) the remainder of the composition a polar solvent, preferably anaqueous solvent containing less than about 5% of at least one VOC andmost preferably containing an absence of VOC's.

In general, the amount of film-forming polymer solid (1 and 2, above)used in the aqueous coating composition ranges from about 15% to about85% by weight of the composition, with a preferred range of at leastabout 40% within this range. In general, the more film-forming polymersolid used in the aqueous coating composition, the greater will be theviscosity of the coating composition and the more favorable will be thedry film characteristics of the final coating.

A low molecular weight film-forming polymer or resin is added in anamount effective to instill resolubility, press performance and wettingcharacteristics to the coating composition before and during depositionand to instill adequate gloss to the dried coating composition(depending upon the type of coating produced, e.g., MAT coatings,Semi-Gloss, etc., the final product will read at least about 10°reflection on a Mallincrodt 60° pocket glossmeter, preferably at leastabout 40° reflection for high gloss). Generally, the amount of lowmolecular weight film-forming polymer will range from about 0% to about99.995% by weight of the combined weight of low and high molecularweight film-forming polymers used in the aqueous compositions andpreferably about 5% to about 95% (more preferably about 10% to about90%) by weight of the combined weight of film-forming polymers.

While not being limited by way of theory, it is believed that the lowmolecular weight film-forming polymer instills gloss to the driedcoatings by virtue of its ability to reflect light from the surface ofthe coating. Because of its relatively small size, the low molecularweight film-forming polymer has a tendency to "lay flat" on the surfaceof the coating. Such an orientation is believed to enhance the abilityof the polymer to reflect light, resulting in a higher gloss value. Highmolecular weight film-forming polymer, because of its relatively largesize, has a tendency not to "lay flat" on a surface, thus enhancing theability of the polymer to absorb light. Consequently, high molecularweight film-forming polymer instills little, if any, gloss to thecoating composition, but instead provides durability and integritycharacteristics to the coating as well as support for the low molecularweight film-forming polymer.

It is thus the combination of low and high molecular weight film-formingpolymers which provides many of the favorable film characteristics. Oneof ordinary skill in the art will recognize to adjust the relativeweight ratio of low and high molecular weight film-forming polymers inorder to instill favorable film characteristics to the dried coatingcompositions.

A high molecular weight film-forming polymer or resin is added to theaqueous coating composition in an amount effective to support the lowmolecular weight film-forming polymer and instill mar resistance, rubresistance, durability and integrity to the dried coating compositionalone or in combination with optional components such as mar resistanceagents and/or hardening agents, among others in a particular coatingapplication. Generally, the amount of high molecular weight film-formingpolymer or resin will range from about 0% to about 99.995% by weight ofthe combined weight of low and high molecular weight film-formingpolymers used in the aqueous compositions and preferably about 5% toabout 95% (more preferably about 10% to about 90%) by weight of thecombined weight of film-forming polymers.

In the aqueous composition according to the present invention, thecombined weight of solids (which includes low and high molecular weightfilm-forming polymers, a surfactant, and optionally, other additives)preferably should comprise no more than about 85% of the total weight ofthe composition and the aqueous solvent should generally comprise noless than about 15% by weight of the composition, and preferably atleast about 30% by weight of the composition. Generally, when the amountof solids is above about 85% by weight of the composition, thecomposition may become too viscous to have adequate transfer. An amountof solids below about 15% is often insufficient to instill adequate filmcharacteristics in the dried coating. Solids include the low and highmolecular weight film-forming polymers, wetting agent or surfactant, mar(scuff) resistant agent, hardening agent, coalescing agent, plasticizingagent and defoaming agent, among other components which are nototherwise considered solvents.

The effective amount of wetting agent or emulsifier used in the presentinvention will generally range from about 0.005% to about 20% or more byweight of the aqueous coating composition. This amount is generallyeffective to provide sufficient wetting of the coating to eliminateleveling problems which may be caused by surface tension duringdeposition onto the inked or uninked layer. The amount and type ofwetting agent or surfactant used will generally depend upon the wettingcharacteristics of the solids without the wetting agent. It is notedthat the film-forming polymers and preferably, the low molecular weightfilm-forming polymer, also may be adapted to instill wettingcharacteristics to the coating composition. One of ordinary skill in theart will recognize to vary the amount and type of wetting agent and theamount of type of film-forming polymer within the teachings of thepresent invention to provide adequate wettability and to eliminatesurface tension in coating compositions according to the presentinvention.

In addition to the above-three components, the aqueous coatingcomposition optionally comprises additional components which may improvemechanical transfer and/or film characteristics of the dried film,especially strength, gloss and durability, among others. Thus, aqueouscoating compositions according to the present invention may employ anyone or more of the following components: a mar (scuff) resistant agent,a hardening agent, a coalescing agent, a plasticizing agent and adefoaming agent, among others.

In the present invention any film-forming polymer typically used incoatings in the printing industry may be used. As used herein, the term"film-forming polymer" is used to describe those high and low molecularweight polymers or resins which can be formulated in aqueous coatingcompositions according to the present invention. These polymers caninclude thermoplastic resins, UV cured and related coating resins whichform a major component of the aqueous coating composition used in thepresent invention. The term film-forming polymer can include oligomericresins which have the ability to be UV or heat polymerized orcross-linked. In the case of UV or heat polymerized coatings, thefilm-forming polymer may be formulated alone or in combination with UVorheat polymerizable monomers.

It is noted that the term "film-forming polymer" embraces a large numberof polymers and related resins used in the aqueous coating compositionsaccording to the present invention and is not simply limited to thethermoplastic resins. Thus, film-forming polymers may include UV curedfilm-forming polymers as well as, in certain cases, thermoset resins,among others. Various mixtures of film-forming polymers may also beused.

The film-forming polymer may be any resinous or polymeric materialincluding for example, poly(vinyl alcohol) and related copolymers,poly(methyl methacrylate) and related (meth)acrylate and acrylatecopolymers, polystyrene and related copolymers, polyester copolymers,nylons, polyamides, polyethylene glycols, polyimides, polycarbonates,epoxies, polyacrylonitriles, polyethylene, polyvinyl, andpolyvinylpyrrolidones among others, including numerous copolymers ofmixtures of monomers used in the above-described resinous materials.Preferably, the film-forming polymer is a relatively hydrophilic orwater-dispersible resin or polymer.

Preferred film-forming polymers for use in the present invention includevarious water soluble or water dispersible copolymers of the followingmonomers: styrene, alpha-methylstyrene, ar-ethylstyrene, vinyltoluene,a,ar-dimethylstyrene, ar-t-butylstyrene, o-chlorostyrene,m-chlorostyrene, p-bromostyrene, 2,4-dichlorostyrene,2,5-dichlorostyrene, among other styrene-containing polymers,vinylnapthalene, alkylesters of (meth)acrylic acid such as n-hexyl(meth)acrylate, ethylbutyl (meth)acrylate, 2-ethyl-hexyl (meth)acrylate,n-octyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate,n-decyl (meth)acrylate, dodecyl (meth)acrylate and similar (meth)acrylicacid esters, alpha,beta-ethylenically unsaturated carboxylic acids, forexample acrylic and methacrylic acid, fumaric acid, itaconic acid andmixtures of these acids, among others. Highly preferred film-formingpolymers for use in the present invention include styrene-(meth)acrylatecopolymers and derivatives thereof. Acidic monomers are preferablyincluded in film-forming polymers to instill wettability characteristicsto the polymer (by forming the free carboxylate which is water soluble).

While the above-described film-forming polymers are preferred for use inthe present invention, it is clearly understood that one of ordinaryskill in the art will be able to adapt other standard and non-standardfilm-forming polymers available in the art to the present methodswithout engaging in undue experimentation.

Preferred low and high molecular weight film-forming polymers used inthe present invention generally have acid numbers ranging from about 5to about 800, a T_(g) ranging from about -75° C. to about 150° C. andaverage molecular weight of about 100 to about 5,000,000 or more;generally about 100 to about 20,000-25,000, preferably about 500 toabout 15,000 for low molecular weight film-forming polymers andgenerally from about 25,000-30,000 to about 5,000,000 or higher,preferably about 100,000 to about 2,000,000 for high molecular weightfilm-forming polymers. The film-forming polymers used in the presentinvention evidence good porosity, and depending upon application, mayhave particle sizes consistent with this porosity of about 1 nanometerto about 20 microns. In addition to the above characteristics, thefilm-forming polymers used in the present invention preferably evidencegood flexibility within the range (both direct impact and reverseimpact) of about 5" per 1 lb. to about 160" per 1 lb.

The low and high molecular weight film-forming polymers used in thepresent invention are most preferably acrylic or acrylic-styrenecopolymers.

Aqueous coating compositions according to the present inventionpreferably evidence acid numbers in the range of about 5 to about 800, apH in the range of about 2 to 12 and a percentage of solids in the rangeof about 15% to about 85% by weight. In the aspect of the presentinvention utilizing high solids content aqueous coating compositions forhigh gloss, the total amount of low and high molecular weightfilm-forming polymer or resin solids ranges from about 42% to about 85%,preferably at least about 50%, by weight of the composition.

In the general aqueous coating compositions used in the presentinvention, the high and low molecular weight film-forming polymerspreferably comprise about 15% to about 85% by weight, and mostpreferably about 42% to about 85% by weight, the remainder being made upof other components as more fully described hereinbelow.

In addition to low and high molecular weight film-forming polymers, theaqueous coating compositions contain an effective amount of a wettingagent or surfactant to compatibilize or emulsify the film-formingpolymers in the aqueous solvent. As used herein, the terms "wettingagent" and "surfactant" describe compounds added to the film-formingpolymers and solvent mixture to emulsify and compatibilize thefilm-forming polymer in the solvent. Wetting agents for use in theaqueous compositions used in the present invention include, for example,OT 75 from American Cyanamid, FC129 from 3M Co., Surfynol 104E by AirProducts & Chemicals, Inc., among a huge number of others. In general,the amount of wetting agent or surfactant included in the aqueouscoatings of the present invention is at least about 0.005%, preferablyat least about 1% to about 20% and most preferably about 1.5% to about10% by weight of the composition, which amounts are generally sufficientfor virtually eliminating surface tension.

In addition to the low and high molecular weight film-forming polymersand wetting agent, the aqueous compositions include an effective amountof a solvent, generally ranging from about 15% to about 80-85% by weightof the composition. Solvents used to formulate the aqueous coatingcompositions according to the present invention include, for example,water and optionally, at least one additional solvent for example,ethanol, methanol, acetone, methylethyl ketone, ethyl acetate, methylacetate, isopropanol, n-butanol, n-butyl acetate, methylchloroform,methylene chloride, toluene, xylene, other aromatic (containing phenylgroups) solvents and mixtures thereof, among others, amyl acetate,numerous ethers, numerous other ketones and alkanes including pentane,cyclopentane, hexane, and cyclohexane, cyclic ethers such astetrahydrofuran and 1,4-dioxane, among other solvents, includingcellosolve, butyl cellosolve acetate, cellosolve acetate, methylcellosolve acetate, butyl cellosolve and ethyl cellosolve.

One important aspect of the present invention involves a method whichcan accommodate very high solids content in aqueous coatings without theneed to adjust viscosity by adding relatively large quantities of aVolatile Organic Compound (VOC). In this method, water is mostpreferably the only solvent utilized in the coating composition. Thiswill allow the method to be practiced in an environmentally compatiblemanner.

In addition to at least one low molecular weight film-forming polymerand one high molecular weight film-forming polymer, a solvent or mixtureof solvents and a wetting agent or surfactant, the aqueous coatingcompositions according to the present invention also include at leastone of the following: mar (scuff) resistant agents, hardening agents,coalescing agents, plasticizer agents and defoaming agents, amongothers, including agents to reduce the coefficient of friction andprovide adequate slip and/or slide angle.

Exemplary mar resistant agents are added to the present invention in anamount effective to provide rub or mar resistance, and generally rangefrom about 0.1% to about 20% by weight of the composition and include,for example, polyethylene and/or paraffin wax (available from S. C.Johnson & Son, Inc.) and Teflon SST-3 from Shamrock Chemicals, amongothers. Exemplary hardening agents are included in amounts generallyranging from about 0.1% to about 10% by weight and include, for example,zinc oxide (available in solution from S. C. Johnson & Son, Inc.), amongothers. Exemplary coalescing agents are included in amounts generallyranging from about 0.1% to about 10% by weight and include, for examplebutyl cellosolve from Union Carbide Corp. and propylene glycol from OlinCorp, among others. These agents serve to render flexibility to films ineffective amounts. Exemplary plasticizing agents are generally includedin amounts effective to produce adequate flexibility and adhesion toprevent chipping and cracking of the film, generally from about 0.1% toabout 10% by weight of the composition. Plasticizing agents include, forexample, Santicizer 160 and Santicizer 141 from Monsanto Corp., amongnumerous other plasticizing agents. Exemplary defoaming agents areincluded in amounts effective to substantially break up any foam thatmay occur during formulation or during the deposition process andgenerally about 0.1% to about 3% by weight of the aqueous composition.Defoaming agents include, for example, Foamkill 875 from CrucibleChemicals Corp. and Balab 3065A from Witco Corp., among others.Exemplary coefficient of friction agents are included in amountseffective to instill adequate slip or slide angle, i.e. generally about0.1% to about 5% by weight. Exemplary coefficient of friction agentsinclude LE 410 from Union Carbide Corp., among other agents.

All of the above-described agents are included in aqueous compositionsaccording to the present invention in amounts effective to substantiallyinstill the final coating with the characteristics sought in adding thecomponent to the composition.

Preferred aqueous coating compositions according to the presentinvention include no more than about 5% by weight Volatile OrganicCompounds (VOC's) and preferably contain an absence of VOC's.

In formulating the aqueous compositions according to the presentinvention, the film-forming polymers and surfactant are first formulatedby mixing in an aqueous solvent. After sufficient mixing, the otheradditives may be added, also followed by mixing. Alternatively, one canadd the film-forming polymers, surfactant and optional additives all atonce to the aqueous solvent, followed by mixing. In certain instances,it may be advantageous to mix low or high molecular weight film-formingpolymer separately with a solvent and optionally, surfactant, beforeadding the other film-forming polymer.

In accordance with the general method of the present invention, anapparatus as depicted in FIG. 1 is useful for carrying out the presentinvention. The apparatus includes a reactor vessel 1 into which isplaced the aqueous coating composition to be deposited onto an inklayer.

The reactor containing coating composition is provided with a heatexchanger 2 for heating or cooling the aqueous coating composition to atemperature above or below ambient temperature. The heat exchangerpreferably takes the form of heating or cooling coils which arepreferably connected to the inside of the reactor or within the reactorchamber. This will allow an efficient transfer of heat into or out ofthe chamber in order to raise or lower the temperature of the aqueouscoating composition.

Reactor 1 may also contain a thermocouple 3 or other temperature sensorto measure the aqueous coating composition within the reactor. Thethermocouple 3 may be operatively connected to the heat exchanger toregulate the exchanger to raise or lower the temperature of the aqueouscoating composition in the reactor. Thermocouple 3 may be set to aspecified temperature corresponding to a predetermined viscosity of theaqueous coating composition utilized. In this aspect of the invention,the thermocouple will regulate the temperature of the coatingcomposition in order to maintain the predetermined viscosity of thecomposition.

Alternatively and preferably, thermocouple 3 is operatively connected toa viscometer 4 which measures and determines the viscosity of theaqueous coating composition. Depending upon the viscosity reading,viscometer 4 signals thermocouple 3 and/or heat exchanger 2 to vary thetemperature of the aqueous coating composition above or below ambienttemperature to initially obtain and thereafter maintain the desiredviscosity.

In addition, viscometer 4 and/or thermocouple 3 may be operativelycoupled to a keyboard or pad 5 for inputting predetermined viscosityand/or temperature values or ranges. Keyboard 5 is connected to amicroprocessor 6 in order to facilitate the maintenance of viscosity ofthe aqueous coating. In response to input from thermocouple 3 and/orviscometer 4, and in accordance with instructions and range values inputvia keyboard 5, microprocessor 6 controls heat exchanger 2 to vary thetemperature inside reactor 1. A display monitor 7 provides visualfeedback of temperature, viscosity settings, etc. to an operator.Inputting viscosity measurements within a pre-determined range for acoating application will enable an operator through microprocessor 6 andthermocouple 3 to control the temperature and, consequently, theviscosity of the aqueous coating composition. Viscometer 4 may serve asa gauge to constantly measure the viscosity of the aqueous coating toensure that the aqueous coating always has the same viscosity as isdesired for a particular application. Microprocessor 6 may be driven bysimple software which can be stored in a read only memory (ROM),erasable, programmable read only memory (EPROM) or other standard memorydevices with the proviso that the software may be easily modified toaccommodate the temperature and/or viscosity measurements desired forthe printing process to be employed. The software may allow for theinput and/or storage of set ranges of viscosities and/or temperatures.

Alternatively, reactor 1 may simply be operatively connected to heatexchanger 2 to manually regulate temperature. Optionally, a thermocouple3 may be operatively connected to heat exchange 2 to provide electronicregulation of the temperature of the aqueous coating in reactor 1.

For a particular coating process, for example, wet-trap in-line,off-line dry-trap, gravure, offset, silk-screen, flexography, theviscosities of a coating composition will fall within certain values.For example, in the case of gravure printing processes, the viscosity ofan aqueous coating composition ranges from about 17 to about 28 secondsmeasured with a #2 Drip Cup. This translates to a viscosity measurementrange of about 19 to about 60 centipoises. In the case of silk screenprinting, this requires a viscosity range of about 12 to about 23seconds (#2 Drip Cup) or a range of about 7 to about 40 centipoises. Inthe case of flexography printing, the viscosity of the aqueous coatingranges from about 20 to about 60 seconds (#2 Drip Cup), or about 30 toabout 140 centipoises. In the case of offset printing, the viscosity ofthe aqueous coating ranges from about 15 to 30 seconds (#3 Drip Cup), orabout 80 to about 225 centipoises.

Thus, the reactor according to the present invention may enable anoperator to input a desired range or ranges of temperatures and/orviscosities which are determined for a particular application and tohave that range or ranges of temperatures and/or viscosities maintainedfor a period sufficient to complete a printing operation. The result isconsistency in depositing aqueous coating compositions regardless of theprinting process or composition used.

FIG. 2 depicts the adaptability of the method of the present inventionfor use in a plurality of printing processes. In FIG. 2, reservoir 8contains a single aqueous coating composition. Coating composition flowsto reactors 9-12 through valves 13-16 which can be opened or closed.Each of the four reactors depicted is capable of maintaining theviscosity of the coating composition within a preset or predeterminedrange, as described above. Depending upon the printing method employed,the transfer of the aqueous composition may be modified simply byadjusting and maintaining the viscosity within a predetermined range.Each reactor may have a different viscosity depending upon the printingmethod employed. Thus, it is possible using the method of the presentinvention to accommodate a plurality of printing processes without theneed to chemically adjust the aqueous coating composition. This is anunexpected result and a clear advance in the printing art.

The following examples are provided to illustrate the present inventionand should not be construed to limit the scope of the invention of thepresent application in any way.

EXAMPLE 1

Experiment to determine the effect temperature has on the viscosity ofan aqueous coating composition and thus the feasability of using thatcomposition in a a number of applications, an aqueous coatingcomposition according to the present invention was formulated from a(meth)acrylic/styrene copolymer. This composition was thereafter exposedto varying temperatures to establish a correlation between viscosity andtemperature.

(1) Preparation of the Aqueous Coating Composition

An aqueous coating composition according to the present invention wasprepared for use in three known printing processes. It contained thefollowing components in the indicated formula.

    ______________________________________                                        Water                   81 grams                                              Wetting Agent (Aerosol 0T 75 by                                                                       9 grams                                               American Cyanamid)                                                            High Molecular Weight Polymer                                                                         105 grams*                                            (Styrenated Acrylic Polymer Emulsion-                                                                 48% solid                                             Joncryl 89 from Johnson Wax)                                                  Low Molecular Weight Polymer Emulsion                                                                 105 grams*                                            (Solid Acrylic Resin 98% non-volatile-                                                                60% solid                                             Joncryl 682 from Johnson Wax)                                                 *-Note that the high molecular weight polymer emulsion                        contains 50 grams of solid and the low molecular                              weight       polymer emulsion contains                                                                    63 grams of                                       solid, the              remainder                                             being aqueous solvent.                                                        ______________________________________                                    

The above coating composition was prepared by agitating a mixture of theabove components in an electronic blender and agitating until thoroughlymixed.

This composition was sufficiently dispersed by homogenizing in ahomogenizing mixture for 5 minutes at which time the temperature of thecomposition was taken using a TEL TRU thermometer. The temperature was82° F. The viscosity of the composition was measured by use of a #3 anda #2 Zahn drip cup and an Aristo Apollo stopwatch. The viscosity of thecomposition at 82° F. was 17 seconds with a #3 cup and 43 seconds with a#2 cup.

(2) Viscosity Relationship

To determine the relationship between viscosity and temperature for theabove-described composition, the temperature of the composition wasvaried and the viscosity of the composition measured at each temperatureinterval. The results of this experiment appear in Table 1, below.

    ______________________________________                                        Temperature (°F.)                                                                  Viscosity (#3 Cup)                                                                           Viscosity (#2 Cup)                                 ______________________________________                                        117° 11 Sec.        26 Sec.                                            110° 11.5 Sec.      27 Sec.                                            104° 12 Sec.        29 Sec.                                            72°  20 Sec.        53 Sec.                                            70°  21 Sec.        59 Sec.                                            64°  26 Sec.        71 Sec.                                            58°  31 Sec.        82 Sec.                                            50°  38 Sec.        101 Sec.                                           42°  47 Sec.        123 Sec.                                           ______________________________________                                    

This experiment evidences that the increase or decrease of temperaturedramatically affects the viscosity of the aqueous coating compositionutilized. We note that within the range of 42° and 117° F. the viscosityvalues which were realized using the instant composition are consistentwith the use of this composition in offset (64° F.-72° F.), gravure(110° F.-117° F.) or flexography (70° F.-117° F.) printing processes.

(3) Gloss Reflection Value (Gloss Value) & Solid Composition

In order to determine the gloss reflection value of the coatingcomposition a uniform coating weight using a Pamarco Inc. hand prooferwas put on a substrate (Westvaco low density SBS with 18 pointcalibration) and measured with a Mallinckodt 60 pocket gloss reader. Thegloss value obtained will vary depending on the absorption rate of thesurface being coated. A high reading of 71.3 gloss reflection value wasobtained. The percentage of solids in the composition was determinedwith use of a Ohaus moisture balance scale which weighs the solids afterdrying out the liquids. This coating composition was 40±2% solid. Thegloss reflection value for this composition is commercially viable forall of the different types of printing processes.

(4) Conclusion

The viscosity of the coating composition was altered by the change intemperature. A decrease in the temperature resulted in higher viscositylevels and an increase in the temperature resulted in lower viscositylevels. While not being limited by way of theory, it is believed that atlow temperatures, the segmental motion in the polymer chain is slowedand/or frozen (depending on the temperature employed), thus increasingthe viscosity. Conversely, when the polymer is heated, the polymer chainundergoes an energizing segmental rotation resulting in decreasedviscosity. Quite unexpectedly, this turns out to be true regardless ofthe additional components one adds to the coating composition.

The results of this experiment evidence the adaptability of the presentmethod in virtually any printing application including offset printing(using for example, a Mann-Roland Rekord MultiColor Press with a tworoll in-line dedicated tower coater), gravure (using for example, a highspeed Goss Roto-gravure, multi-unit printing press with engraved gravurecylinder), and flexography (using for example, a Manhasset flexographyprinting press with a flexographic 2-roll transfer system)--even thougheach process has significantly different viscosity requirements and thepresent art cannot accommodate the same formulation as easily andefficiently as the present invention. Inasmuch as the useful offsetrange is 15 to 30 seconds with a #3 cup; the useful gravure range is 17to 28 seconds with a #2 cup, and the useful flexography range is 20 to60 seconds with a #2 cup, the present method can accommodate each ofthese printing processes to produce commercially viable results. We notethat the viscosity of the composition at the starting temperature wasoutside of the useful range for gravure until it was sufficiently heatedto bring it within the gravure range. Higher temperatures would beneeded to lower the viscosity of the composition even further.

EXAMPLE 2

In order to determine the effect temperature variations have on addedsolids (resins & emulsions), through the use of this invention, on theviscosity level of an aqueous coating and thus, the feasibility of usingthat coating in any printing application, a specific resinouscomposition comprising an acrylic methacrylic styrene copolymer wasused. This composition was altered by the addition of solids and thesenewly formed compositions were exposed to varying temperatures.

(1) Preparation of the Aqueous Coating Composition with AdditionalSolids

Coating compositions having the following recipes were prepared as acoating liquid for application in all the printing processes.

    ______________________________________                                        (A)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                105 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 135 grams                                             Same as Example 1                                                        (B)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                174 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 135 grams                                             Same as Example 1                                                        (C)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                105 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 165 grams                                             Same as Example 1                                                        (D)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                150 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 165 grams                                             Same as Example 1                                                        ______________________________________                                    

The above coating compositions were prepared by agitating the mixturesof the above components in an electronic blender and agitating untilthoroughly mixed.

(2) Temperature Variations & Viscosity Relationship

The various coating compositions were cooled and heated to determine therelationship between temperature, viscosity, and increased solids.

    ______________________________________                                        Composition                                                                             Temp. (°F.)                                                                      Visc. (#3 Cup)                                                                            Visc. (#2 Cup)                                ______________________________________                                        A         132°                                                                             13 Sec.     28 Sec.                                                 83°                                                                              25 Sec.     67 Sec.                                                 67°                                                                              38 Sec.     99 Sec.                                       B         166°                                                                             10 Sec.     22 Sec.                                                 160°           23 Sec.                                                 140°           27 Sec.                                                 120°                                                                             15 Sec.     38 Sec.                                                 119°                                                                             15 Sec.                                                             118°           38 Sec.                                                 110°                                                                             15 Sec.                                                             80°                                                                              35 Sec.     87 Sec.                                       C         148°           24 Sec.                                                 138°                                                                             14 Sec.                                                             136°           24 Sec.                                                 128°                                                                             15 Sec.                                                             100°                                                                             23 Sec.     63 Sec.                                                 82°                                                                              38 Sec.     100 Sec.                                                70°                                                                              50 Sec.     137 Sec.                                                60°                                                                              66 Sec.     176 Sec.                                                50°                                                                              99 Sec.     243 Sec.                                      D         155°           26 Sec.                                                 140°           42 Sec.                                                 111°                                                                             26 Sec.     69 Sec.                                                 70°                                                                              90 Sec.                                                   ______________________________________                                    

(3) Gloss Reflection Value & Solid Composition

Using the name techniques (tests) as above, the following glossreflection values & solid compositions were obtained without affectingthe mechanical transfer and the film formation properties andcharacteristics of the coatings.

(A) Gloss 82.3 High Solids 43%±2%

(B) Gloss 86.1 High Solids 47%±2%

(C) Gloss 88.5 High Solids 45%±2%

(D) Gloss 90.5 High Solids 50%±2%

(4) Conclusion

One may increase solids (both high and low molecular weight resinsand/or emulsions), yet produce formulations which are in keeping withthe present invention, in particular, the ability to provide workableviscosities having acceptable mechanical transfer for use in printingprocesses according to the present invention. It is noted that theuseful offset range is 15 to 30 seconds with a #3 cup; the usefulgravure range is 17 to 28 seconds with a #2 cup, and the usefulflexography range is 20 to 60 seconds with a #2 cup evidencing that thepresent invention may be used in numerous printing processes to producecommercially viable results.

One may also increase gloss reflection value. Workable viscosity for usein printing processes may be managed through temperature control despiteincreased solids which would otherwise negatively impact mechanicaltransfer and take the composition out of workable mechanical applicationranges desirable for use in the printing processes.

EXAMPLE 3

Experiment to determine the effect of maintaining the same temperatureover a period of time on viscosity of aqueous coating compositionsaccording to the present invention. Test compositions were those fromExample 2, above. For each composition, the temperature was maintainedfor a period of time to determine whether or not it was possible tomaintain the viscosity of a composition by maintaining the temperature.

(1) Aqueous Coating Compositions Used-Four Formulations as follows:

    ______________________________________                                        (A)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                105 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 135 grams                                             Same as Example 1                                                        (B)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                174 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 135 grams                                             Same as Example 1                                                        (C)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                105 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 165 grams                                             Same as Example 1                                                        (D)  Water                   81 grams                                              Wetting Agent (same as Example 1)                                                                     9 grams                                               High Molecular Weight Polymer Emulsion                                                                150 grams                                             Same as Example 1                                                             Low Molecular Weight Polymer Solution                                                                 165 grams                                             Same as Example 1                                                        ______________________________________                                    

The above coating compositions were prepared by agitating the mixturesof the above components in an electronic blender and agitating untilthoroughly mixed.

(2) Temperature Maintenance & Viscosity Relationship

The various coating compositions were maintained at a constanttemperature for 120 hours and the viscosity was checked every 6 hours inorder to determine the relationship between temperature, viscosity andtime.

    ______________________________________                                        Composition                                                                            # Measurements                                                                            Temp.     Visc. (#3 or #2 Cup)                           ______________________________________                                        A        20          83°                                                                              25 Sec. (#3)                                            20          132°                                                                             28 Sec. (#2)                                   B        20          120°                                                                             15 Sec. (#3)                                            20          160°                                                                             23 Sec. (#2)                                   C        20          100°                                                                             23 Sec. (#3)                                            20          136°                                                                             24 Sec. (#2)                                   D        20          111°                                                                             26 Sec. (#3)                                            20          155°                                                                             26 Sec. (#2)                                   ______________________________________                                    

(3) Gloss & Solids

Same test as Example 2 gave same results a set forth in Example 2, aspreviously described.

Does not affect mechanical transfer or film formation characteristics ofcoatings.

(4) Conclusion

Maintaining the temperature of aqueous coatings according to the methodof the present invention resulted in constant viscosity, even at highsolid content. The result was mechanically workable solutions.

The present invention ameliorates concerns regarding changes inviscosity which often occur within 48 hours after the formulation ismade and before the composition reaches an equilibrium (molecularstructure of particles still in excitable state and not at equilibrium).

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are preferred by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

I claim:
 1. A method for depositing an aqueous coating composition ontoan ink layer or uninked surface in a printing process comprising:1).Depositing a first layer of ink onto a surface to be coated; 2). Dryingsaid ink layer; 3). Determining a desired viscosity of an aqueouscoating composition to be deposited onto said ink layer or said surface,said composition comprising:a. about 15% to about 85% by weight of afilm-forming polymer, said film-forming polymer comprising a mixture ofhigh molecular weight and low molecular weight film-forming polymers,said mixture of polymers comprising about 5% to about 95% by weight of ahigh molecular weight film-forming polymer and about 5% to about 95% byweight of a low molecular weight film-forming polymer, said highmolecular weight film-forming polymer having an average molecular weightranging from about 30,000 to about 5,000,000 and said low molecularweight having an average molecular weight ranging from about 100 toabout 25,000; b. an amount of a wetting agent effective to substantiallyeliminate levelling problems after deposition caused by surface tension;and c. the remainder of said composition comprising a mixture of wateror water and at least one solvent in the form of a volatile organiccompound; 4). Determining the temperature above or below ambienttemperature at which said composition attains the viscosity determinedin step 3); 5). Maintaining the viscosity of said composition at thetemperature determined in step 4); and 6). Depositing onto said inklayer or said surface said aqueous coating composition at saidtemperature.
 2. The method according to claim 1 wherein said compositionincludes one agent selected from a mar resistant agent, a coalescingagent, a hardening agent, a plasticizing agent, a defoaming agent ormixtures thereof.
 3. The method according to claim 1 wherein saidfilm-forming polymer is a thermoset resin, a UV-cured resin or athermoplastic resin.
 4. A method for depositing an aqueous coatingcomposition onto an ink layer or uninked surface in a wet-on-wetprinting process comprising:1). Depositing a first layer of hydrophobicink onto a surface to be coated; 2). Determining a desired viscosity ofan aqueous coating composition to be deposited onto said ink layer orsaid uninked surface, said composition comprising:a. about 15% to about85% by weight of a film-forming polymer, said film-forming polymercomprising a mixture of high molecular weight and low molecular weightfilm-forming polymers, said mixture of polymers comprising about 10% toabout 90% by weight of a high molecular weight film-forming polymer andabout 10% to about 90% by weight of a low molecular weight film-formingpolymer, said high molecular weight film-forming polymer having anaverage molecular weight ranging from about 30,000 to about 5,000,000and said low molecular weight having an average molecular weight rangingfrom about 100 to about 25,000; b. an amount of a wetting agenteffective to substantially eliminate levelling problems after depositioncaused by surface tension; and c. the remainder of said compositioncomprising a mixture of water or water and at least one solvent in theform of a volatile organic compound; 3). Determining the temperatureabove or below ambient temperature at which said composition attains theviscosity determined in step 2); 4). Maintaining the viscosity of saidcomposition at the temperature determined in step 3); and 5). Depositingonto said ink layer or said uninked surface said aqueous coatingcomposition at said temperature.
 5. The method according to claim 4wherein said composition includes one agent selected from a marresistant agent, a coalescing agent, a hardening agent, a plasticizingagent, a defoaming agent or mixtures thereof.
 6. The method according toclaim 4 wherein said film-forming polymer is a thermoset resin, aUV-cured resin or a thermoplastic resin.
 7. A process for enhancing thesolids content of a dry-film produced in a printing process bydepositing a high solids content aqueous coating composition onto an inklayer or uninked surface to instill favorable dry-film characteristics,including high gloss, comprising the steps of:1). Preparing a highsolids content aqueous coating composition for coating an ink layer oruninked surface in a printing process, said composition having aviscosity above a range useful in said process at ambient temperature,said composition comprising:a. about 42% to about 85% by weight of afilm-forming polymer, said film-forming polymer comprising a mixture ofhigh molecular weight and low molecular weight film-forming polymers,said mixture of polymers comprising about 5% to about 95% by weight of ahigh molecular weight film-forming polymer and about 5% to about 95% byweight of a low molecular weight film-forming polymer, said highmolecular weight film-forming polymer having an average molecular weightranging from about 30,000 to about 5,000,000 and said low molecularweight having an average molecular weight ranging from about 100 toabout 25,000; b. an amount of a wetting agent effective to substantiallyeliminate levelling problems after deposition caused by surface tension;and c. the remainder of the composition comprising a mixture of water orwater and at least one solvent in the form of a volatile organiccompound; 2). Depositing a first layer of ink onto said uninked surfaceto be coated; 3). Determining a desired viscosity of said aqueouscoating composition to be deposited onto said ink layer or said uninkedsurface; 4). Determining the temperature above ambient temperature atwhich said composition attains the viscosity determined in step 3); 5).Maintaining the viscosity of said composition at the temperaturedetermined in step 4); and 6). Depositing onto said ink layer or uninkedsurface said aqueous coating composition at said set temperature.
 8. Theprocess according to claim 7 wherein said components a, b and c compriseat least about 50% by weight of said composition.
 9. The methodaccording to claim 7 wherein said low molecular weight film-formingpolymer and said high molecular weight film-forming polymer eachcomprise at least about 25% by weight of said formulation.
 10. Themethod according to claim 7 wherein said composition includes one agentselected from a mar resistant agent, a coalescing agent, a hardeningagent, a plasticizing agent, a defoaming agent or mixtures thereof. 11.The method according to claim 7 wherein said film-forming polymer is athermoset resin, a UV-curable resin or a thermoplastic resin.
 12. Themethod according to claim 7 wherein said film-forming polymer is anacrylic resin or styrene-acrylic resin.
 13. A process for coating acomposition onto an ink layer or uninked surface in a printing processcomprising the steps of:1). Preparing a composition comprising:a. about15% to about 85% by weight of a film-forming polymer, said film-formingpolymer comprising a mixture of high molecular weight and low molecularweight film-forming polymers, said mixture of polymers comprising about5% to about 95% by weight of a high molecular weight film-formingpolymer and about 5% to about 95% by weight of a low molecular weightfilm-forming polymer, said high molecular weight film-forming polymerhaving an average molecular weight ranging from about 30,000 to about5,000,000 and said low molecular weight having an average molecularweight ranging from about 100 to about 25,000; b. an amount of a wettingagent effective to substantially eliminate levelling problems afterdeposition caused by surface tension; and c. a mixture of water or waterand at least one solvent in the form of a VOC; 2). Determining a desiredviscosity of said composition to be deposited onto said ink layer orsaid uninked surface; 3). Determining the temperature above or belowambient temperature at which said composition attains the viscositydetermined in step 2); 4). Maintaining the viscosity of said compositionat the temperature determined in step 3); and 5). Depositing onto saidink layer or said uninked surface said composition at said settemperature.
 14. The method according to claim 13 wherein thecomposition comprises no more than about 5% by weight VOC.
 15. Themethod according to claim 13 wherein said low molecular weightfilm-forming polymer and said high molecular weight film-forming polymereach comprise at least about 10% by weight of said formulation.
 16. Themethod according to claim 13 wherein said surfactant comprises about0.005% to about 10% by weight of said formulation.
 17. The methodaccording to claim 13 wherein said composition includes one agentselected from a mar resistant agent, a coalescing agent, a hardeningagent, a plasticizing agent, a defoaming agent or mixtures thereof. 18.The method according to claim 13 wherein said solvent is water.
 19. Themethod according to claim 13 wherein said film-forming polymer is athermoset resin, a UV-cured resin or a thermoplastic resin.
 20. Themethod according to claim 13 wherein said film-forming polymer is anacrylic resin or styrene-acrylic resin.